\begin{tikzpicture}[>=Stealth, scale=0.8]
    \draw [->] (-2.5, 0) -- (2.5, 0) node[anchor=west] {$x$};
    \draw [->] (0, -2.5) -- (0, 2.5) node[anchor=east] {$y$};
    \node at (0.3, -0.3) {$O$};

    \draw[->, thick] (0, 0) -- (-1.5, 1.5) node[anchor=east] {$Z$};
    \draw [dashed] (-1.5, 0) -- (-1.5, 1.5) -- (0, 1.5);
    \node at (-1.7, -0.3) {$-1$};
    \node at (0.3, 1.5) {$1$};

    \draw[rotate=120, ->, thick] (0, 0) -- (-1.5, 1.5) node[anchor=east] {$Z'$};
    \draw [rotate=135,->] (1, 0) arc (0:120:1);
    \node [rotate=90, fill=white, inner sep=0] at (-1, 0) {$120^\circ$};
\end{tikzpicture}
